Electromagnetic operator



June 24, 1958 G. CURRIE ELECTROMAGNETIC OPERATOR 5 Sheets-Sheet 1Original Filed Oct. 3, 1951 lNVENTOR gilberf Currie.

Y M5. W

ATTORNEY June 24, 1958 G. CURRIE ELECTROMAGNETIC OPERATOR 5 Sheets-Sheet2 Original Filed Oct. 3. 1951 INVENTOR' Gilbert Currie. BY W5 ATTORNEYWITN ESSES June 24, 1958 G. CURRIE 2,840,769

ELECTROMAGNETIC OPERATOR Original Filed Oct. 3, 1951 3 Sheets-Sheet 3 I35 34 g l 35 28 27 I50 l5b INVENTOR Gilbert Currie ATTORN E UnitedStates Patent ELECTROMAGNETIC OPERATOR Gilbert Currie, Williamsville, N.Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa.,a corporation of Pennsylvania Original application October 3, 1951,Serial No. 249,497,

now Patent No. 2,747,698, dated May 29, 1956. Divided and thisapplication August 23, 1955, Serial No. 530,162

6 Claims. (Cl. 317-198) This invention is a division of the applicantscopending application, Serial No. 249,497, now Patent No. 2,747,698,entitled Brake, filed October 3, 1951, and assigned to the assignee ofthis invention. The aforesaid application relates generally to brakesand is particularly directed to a brake which compensates brake wear,misalignment of parts and requires no adjustment through out the usefullife of the brake shoes or lining.

The divisional subject matter of this application is directedparticularly to an electromagnetic operator employed in the brake of theparent application for releasing the brake, that is, disengaging thebrake shoes from the brake wheel by energization of the electromagnet.

In certain of its general aspects this invention is related to certainfeatures of applicants Patents 2,514,378 and 2,685,945 and in other ofits aspects this invention is related to applicants Patent 2,752,010,all the aforesaid items being assigned to the assignee of thisinvention.

This invention, in one form of embodiment is illustrated in connectionwith an electric brake of the double block type in which the movingsystem of the electromagnet is spring loaded to apply the braking torqueand the moving system is electromagnetically operated against the springor braking torque to move the brake to disengaged position.

The present invention by way of illustration, but without limitation isillustrated in application to a double block type of brake wherein theutility of the novel features of the electromagnetic operator arereadily apparent.

In the usual case, double block brakes comprise a brake wheel and havebrake arms on opposite sides of the brake wheel, which carry the brakeshoes adjacent their extremities. The brake is set by a compressionspring and a link system connecting the free extremities of the brakearms. This forces the brake arms together, and the brake is usuallyreleased by means of a bell crank having its middle fulcrum on the brakearm extremity adjacent the compression spring, and one end thereofattached to the link. Force applied in the proper direction to theremaining extremity of the bell crank, drives the free extremities ofthe brakearms apart and releases the brake. Frequently on double blockbrakes, the bell crank is actuated by a solenoid.

Most brakes of this general type have three adjustments, one for varyingthe torque, and hence, for varying the braking and releasing effort byvarying the amount of spring compression, one for equalizing the shoeclearances, usually by means of separate adjustments on the shoes, andthe third for adjusting the stroke or travel of the solenoid orelectromagnet plunger or armature.

While these adjustments may vary for different types of brakes, they areessentially the same. In the typical case, after the brake is mounted inposition, it is necessary to make most, and usually all of theseadjustments, and the successful operation of the brake depends upon theskill with which the adjustments are made.

These adjustments, under ideal working conditions,

2,840,769 Patented 7 June 24, 1

2 ordinarily require a fair degree of skill, to obtain the mostefiicient operation of the brake. In many instances, however, brakes areinstalled in out-of-the-way places where lighting is poor and where thespace is cramped. Under these conditions, it is extremely difiicult tomake the three adjustments hereinabove mentioned. In such instances, thebrake is usually always out of adjustment and maximum operatingetficiency is therefore not obtained. I

Initial adjustments, however, hold only for the thickness of the newbrake shoe lining. As the brake is used and the linings are Worn, thebrake is continuously moving out of adjustment. When the lining has wornan amount equal to the initial shoe clearances, the travel of thearmature or solenoid plunger has been doubled, and it is usuallynecessary to readjust the brake to restore the travel to its originalamount. If the adjustments are not made at the proper time, or are notproperly made, brake failures evidenced in excessive heating and burnedout solenoid coils may result.

Due to the facility of adjustment of the brake of this invention at thetime of manufacture, and due to the fact that this brake automaticallyadjusts itself during operation, it will be appreciated that brakefailures may be minimized with no maintenance time and effort beingrequired other than to replace worn out lining. In accordance withanother feature of this invention, movement of certain specified partsof the brake to given limit positions may be utilized by suitable,visual, or audible indicating means, to signal the operator that thebrake must be relined.

The certain specified parts referred to in the preceding paragraph mayinclude the brake operating lever or levers and the plunger of thesolenoid or electromagnet used to operate the brake. As the brake liningwears the angular position of the brake operating lever changes in suchsense as to continuously move the plunger or armature away from thecore. This increases the open gap position of the armature which mayincrease to the point where the flux linkage between the core andarmature is insufficient to attract the armature to the core and releasethe brake. The electromagnet assembly of this invention overcomes thisproblem in the provision of a linkage between the electromagnet armatureand the brake operating lever system affording a disengageableconnection between the armature and the brake lever system such that thelength of the armature stroke is maintained constant throughout therange of brake lever angular positions with brake lining thicknessvariations over the useful life of the brake lining.

In accordance with the foregoing considerations, it is generally oneobject of this invention to provide an electromagnetic operator of thecharacter generally referred to, which is simple in its elements withrespect to operational requirements and consistent in its operation.

It is also a general object of this invention to provide anelectromagnetic operator of the character referred to which may befactory adjusted and which requires no adjustment after it is placed inoperation.

A more specific object of this invention is to provide anelectromagnetic operator of the class generally referred to in which thedistance of travel of the plunger or electromagnet armature in operatinga member to be controlled is constant and is always confined to the samedefinite path, irrespective of change in position of the controlledmember to thereby eliminate overtravel and side pull of the plunger orarmature.

The foregoing statements are merely illustrative of the various aims andobjects of this invention. Other objects and advantages will becomeapparent from a study of the following specification, when considered inconjunction with the accompanying drawings, in which:

Figure 1 is a longitudinal sectional view of a brake assembly embodyingthe features of this invention.

.Figure 2 is a bottom view of Figure 1, illustrating certains details ofthe brake linkage.

Fig. 3 is an end view of the brake assembly of Figure 1, as viewed fromthe right end of the brake, which view illustrates certain otherdetailed features of the brake linkage and general construction, and

Figure 4 is a view taken on section line IVIV of Figure 3.

The novel aspects of the electromagnetic operator of this invention willbe better understood from a consideration of the details of the brakeassembly in which it is applied.

- The various components of the brake assembly are mounted upon asupport or base section comprising a pair of spaced parallel angles 1.These angles are suitably spaced apart to receive therebetween thevarious levers of the brake linkage system. At the right end of the baseof the brake, as viewed in Figures 1 and 2, there are mounted two brakearm assemblies, generally designated, 2 and 3. These brake armassemblies comprise a pair of similar levers, respectively designated 2aand 2b, and 3a and 311. Brake arm levers 2a and 2b, are pivotallyconnected between the vertical flanges of the base angles by means of ashaft 4, provided with reduced diameter, threaded end sections, whichclear through suitably positioned holes in the mentioned verticalflanges of the base section, and which are secured by means of nuts 5,which thread thereover. Brake arms 3a and 3bare similarly pivotallysecured between the vertical flanges of the base angles by means of ashaft 6, the ends 'of which extend through the vertical flanges'and havethreaded thereover nuts 7.

These brake arm assembly pivot mountings, for the respective brake armassemblies,are arranged in suitably spaced relation along the basesection and as seen in Figure 1, vertical extensions of the brake armsproject upwardly on each side of a brake wheel 8.

Brake shoes 9 and 10 are respectively pivotally connected to the upperextremities of the respective brake arm assemblies 2 and3 by means ofrespective pivot pins 11 and 12, which extend through respective bosses13 and .14 on the brake shoes and engage the upper ends of therespective levers of the brake arm assemblies. As a general rule,suflicient frictional restraint in this pivotal mounting of the brakeshoes on the brake arms is provided so that the shoes do not rotate dueto their own weight, whenever the brake arms are moved to brake releasedposition. The brake shoes are properly aligned by movement of the brakearms to a position in which the brake shoes engage the wheel. Thefrictional restraint is overcome due to the force of this engagement andthe brake shoes are properly oriented with respect to the wheel, andmaintain this position in the brake released position.

- A lever assembly generally designated 15, is connected to each brakearm assembly at a point on each assembly which is displaced from therespective points of pivoting of the brake arm assemblies on the base.The point of connection of lever assembly 15, with brake arm assembly 2is designated 16, which is represented in a pin extending through bothsections 15a and 15b of lever 15, and terminating in the respectivelevers 2a and 2b of brake arm assembly 2. A pin 17, which extendsthrough, and is secured in'both lever sections 15a and 15b of the leverassembly 15, is provided with a flat bottom face 18, and the verticaldimension as seen in Figure 1, of the respective ends of the pin is suchas to 'fit int o and slidably engage the edges of respective slots 19,provided in the remaining corresponding extremities of the brake armassembly 3.

As will be seen by reference to both Figure 1 and Figure 2, leverassembly 15, comprises a pair of spaced, parallel straight bars, 15a and15b, of rectangular cross section, for reasons of structural simplicity.In view of this, provision is made through respective holes 21 and 22 inthis lever assembly to clear the brake arm pivot pins 4 and 6. Thusit'will be appreciated that angular movement of lever assembly 15 isobtainable within the limits imposed by the clearance of the respectiveholes 21 and 22 about the respective pivot .pins 4 and 6.

Since it is desirable in operation of the brake to minimize conditionsof back lash due to lost motion in certain of the connections, a spring23 is connected between pins 24 and 25, respectively mounted on leverassembly 15, and brake arm assembly 3. This spring is under tension andconsequently tends to move the pins 24 and 25 together. In so doing thebrake arm assembly 3 is biased counterclockwise, as viewed in Figure 1,to a position in which the bottom edge of slot 19, abuts the flat face18 on the bottom side of pin 17. Also cross piece or trunnion pin 28whose ends are carried by lever assembly 15 is biased upwardly againstthe shoulder on the spindle 26.

A frictional connection is provided between the lever assembly 15 andbrake arm assembly 2, for the purpose of providing an adjustableconnection of lever assembly 15 with brake arm assembly 2 through whichlimited torque may be applied to actuate the brake arm assembly 2 in adirection to release the brake shoe 9 from the wheel, but which yetprovides for relative angular movement between the lever assembly 15 andbrake arm assembly 2, when the lever assembly is moved counterclockwise,as viewed in Figure 1, to apply the brake shoe to the wheel. Thisfrictional connection comprises a pair of friction washers or plates 20,which are respectively disposed between the adjacent levers of the brakearm assembly 2 and the lever assembly 15, and further comprises a pairof spring washers 20a, disposed between the adjacent faces of levers 15aand 15b. A compression spring 2% disposed between these spring washersthrusts the levers 15a and 15b apart as seen in Figure 2 and securelyengages the respective levers with the respective friction plates orwashers 20.

With the construction thus far described, it a downward' force isexerted on the left-hand end of lever assembly 15, the lever assemblywill tend to pivot about the center of shaft 4 due to the frictiondevice just described and will move in a counterclockwise direction asviewed in Figure 1. Pin 17 will therefore tend to move downwardly andpin 16 will tend to move upwardly. These forces cause the respectivebrake ann assemblies to rotate about their respective pivot pins 4 and6, brake arm assembly 2 rotating counterclockwise and brake arm assembly3 rotating clockwise, to apply the respective shoes to the brake wheel.Since the holes 21 and 22 in lever assembly 15 are provided, it will beappreciated that this small counterclockwise movement of the leverassembly will not bev obstructed by the respective brake arm assemblypivot .pins 4 and 6.

For a particular location of the wheel, for example, a location of thewheel exactly on the designed center line of the brake, as shown inFigure 1, the lever assembly 15, at the time the brake shoes engage thebrake wheel, will occupy a given angular position with respect to therespective brake arms. However, if the brake wheel should be to theright or to the left of this particular position, the leverassembly 15would occupy a diiterent angular position with respect to the brake armsthan that which is illustrated. Under these conditions the angularrelationship of the lever assembly 15 with respect to brake arm assembly2, must change in an amount dictated by the degree of misalignment andthis is physically possible since the braking force which is applied tothe left end of the lever assembly 15 is. sufficient to overcome thefriction between lever assembly 15 and brake arm assembly 2.

It will thus be appreciated that braking torque is applied to the brakearms through the connection of the lever system 15 to the respectivebrake arms at the two points 16 and 17. By proper selection of thevarious lever arms which are involved in this mechanical linkage, it ispossible to obtain equal braking torques as will be shown hereinafter.

It is desirable, although not absolutely .necessary in this instance,that any misalignment of the brake wheel with respect to the designedcenter line of the brake, resulting in angular displacement of the leverassembly 15, shall not result in vertical displacement of the left endof this lever assembly. In the applicants aforesaid copendingapplication Serial No. 249,498, if such vertical displacement occurs,due to such misalignment, the travel of the brake engaging and brakereleasing mechanism is changed to some new value. To offset such achange it would then be necessary to efiect an adjustment of the brakemechanism to restore the travel of the :brake operating mechanism to itsinitial condition.

However, in the present brake such vertical displacement merely changesthe relative positions of certain components of the brake releasingmechanism, yet to be described and does not affect the travel of suchmechanism. Hence, in this instance such displacement will not disturbbrake releasing movement although calibration for a given braking torquemay be changed to a small extent.

The illustrated linkage system, however, is relatively proportioned insuch a manner that the left end of the lever assembly 15 does not moveeven though misalignment of the brake wheel with respect to the designedcenter line of the brake may exist.

This will be appreciated from a consideration of the respective leverarms for the condition in which the brake wheel is moved to the left ofthe designed center line of the brake. Under this condition both brakearm assemblies will be rotated in a counterclockwise direction asviewed. Consequently, both pins 16 and 17 will move upwardly, and theratio of the movement of the pin 16 to the pin 17 will be proportionalto the ratio of the dimension y to the dimension x, illustrated in thedrawings. If this ratio is properly selected, the distance traveled byeach pin will correspond to the distance between the sides of an anglesubtended by the angular movement of the lever system 15, which anglehas its vertex at the left end of the lever system.

This might be realized as follows: When the lever assembly 15 is rotatedabout its left end, the pins 16 and 17 move an amount corresponding tothe ratio y to x of the respective moment arms y and x. Consequently, ifthe ratio of y to x is made equal to the ratio of y to x, any moment ofthe wheel to the right or to the left of the designed center line willresult in a rotation of lever assembly 15 about its left end, and thepoint to which the force is applied to obtain braking torque will remainstationary and the adjustment or calibration of the brake will not bechanged.

The brake is applied by applying a downward force to the left end of thelever assembly 15 along the line of action P to release the brake withthe construction provided, an upward force is applied to this samepoint. Because of the friction produced by the spring pressure engagingthe respective levers of the lever assembly and the brake arm assemblywith friction plate 20, upward, force on the left end of the leverassembly 15, rotating this lever assembly in a clockwise direction, willtend to move the brake arm assembly 2 angularly, at the same time thebrake arm assembly 3 is moved angularly, in directions to lift the brakeshoes from the wheels. The releasing torque, which moves brake armassembly 2 away from the brake wheel is applied thereto through thementioned frictional connection between the lever assembly 15 and thebrake arm assembly 2. Since there is no restraining force on this brakearm assembly, other 6 than bearing friction, for this direction ofmovement, it will be appreciated that a relatively small frictionalforce will be sufficient to accomplish this end.

The pin 17, as indicated by dimensions designated x, is disposed midwaybetween the respective brake arm pivot pins 4 and 6, and, inasmuch asrotation of the lever assembly 15 takes place about the axis of the pin4 during brake releasing movement, it will be appreciated that bothbrake shoes are moved, in the same amount, away from the brake wheel 8.

With the lever arrangement illustrated, a downward force such as P onthe left end of lever assembly 15 produces equal and opposite forces onthe brake shoes. Taking moments about the respective pins 16 and 17, thedownward force on pin 17 is equal to:

Since as earlier described herein, the ratio of y'to x was made equal tothe ratio of y to x', it will be appreciated that the product of these,inversely related ratios in the final expression, will be unity, whichindicates that the torques are equal.

The mechanism for removing lever assembly 15 in brake engaging and brakereleasing directions includes a spindle 26 which is pivotally secured atits bottom end to the left end of lever assembly 15 by means of atrunnion pin 27. Trunnion pin 27 straddles the distance between thelever sections 15a and 15b and is provided with a hole therethrough,which is normal to the trunnion axis, through which the bottom threadedend of spindle 26 is fitted. Spindle 26 is secured against rotation inthe trunnion 27 by means of a pair of nuts 28 which are threadedthereon, and which clamp the trunnion therebetween.

The spindle extends upwardly through a central cylindrical opening 29 ina magnet housing 30. The magnet housing is comprised of an upper part 31and a lower part 32. These two sections are secured together on theirmating faces by means of bolts 33. This magnet housing is supported by apair of angle sections 34 which are bolted to the vertical flanges ofthe base angles 1 and form a platform across their horizontal flanges onwhich the lower part 32 of the magnet housing is seated and secured bybolts 35.

Spindle 26 is slidably fitted through an externally threaded bushing 36which is rotatably mounted in the central opening of a cover plate 37which is bolted across the top of the opening 29 in the magnet housing31. A pair of sleeves 38 and 39, respectively, are fitted over thespindle 26. Sleeve 38 abuts the upper trunnion nut 28 and sleeve 39abuts the top end of the sleeve 38. This assembly of sleeves is securedaxially of spindle 26 by means of a spring washer 40 which is fittedover the spindle 26 in abutting relationwith the upper end of sleeve 39.it

Spring washer 40 is secured in its position axially of spindle 26 bymeans of a clamp 41 which clamps over a reduced diameter section ofspindle 26 and abuts the upper end of the spring washer 40. A secondspring washer 42 threads over the externally threaded portion of bushing36 and is drilled and tapped at one point adjacent its peripheral edgeto receive a short rod 43, the bottom end of which threads into thementioned threaded hole. The upper end of this rod projects through ahole 44 in cover plate 37.

-Springs 45 and 46 are compressed between respective shoulders on springwashers 40'and 42. The compressive force thrusting the lower springwasher 46 downwardly, which by reason of its secure connection withrespect to the spindle. 26, drives the spindle 26 downwardly. Thisdownward thrust of the spindle through trunnion pin 27 rotates leverassembly in a counterclockwise direction as viewed in Figure 1, drivingpin 17 downwardly and pin 16 upwardly. As, previously described, thismovement engages the respective brake shoes with brake wheel 8,

The force of engagement of the brake shoes with the brake wheel isadjustable by the threaded bushing 36. It will be recalled that bushing36 is rotatably mounted in the cover plate 37. The end of this bushingwhich projects through the cover plate is provided at 47 with flatsurfaces to receive awrench. Rotation of the bushing through theapplication of a wrench thereto moves the upper spring washer 42 up anddown along the threaded portion of the bushing. By reason of theconnection of rod 43 with the cover plate through the hole 44, springwasher 42 is stationarily secured against rotation at the time thatbushing 36 is rotated. Consequently, the only direction of freedom ofthis spring washer is axially of the threaded bushing.

Movement of this bushing controls the degree of compression of. springs45 and 46 and consequently, controls the braking torque. The amount ofbraking torque may be indicated by suitable marks along the rod 43arranged to indicate the value of torque when the r spective marks areadjacent the upper edge of a dust seal 48.secured to the top cover 37about the rod 43. The indicated position corresponds to 100% brakingtorque.

Means for mechanically releasing the brake assembly is provided in a nut49, which threads over the upper end of spindle 26. By rotating this nutdownwardly along spindle 26, the nut is brought into engagement with theupper end of bushing 36. Continued rotation of the nut in this directionthen pulls spindle 26 upwardly through the magnet housing and moves thelever assembly 15 in a clockwise direction, which as previouslydescribed, moves the brake arm and brake shoes in a direction to releasethe shoes from the brake wheel.

As earlier noted in this discussion, this brake assembly isself-compensating for misalignment of the brake wheel with respect tothe designed center line of the brake and for wear of the brake lining.This is accomplished, in general, by an actuating means embodying alinkage which is normally disengaged from the spindle 26 and whichoccupies a position adjacent the path of movement of the spindle suchthat displacement of the spindle longitudinally of its axis, does notvary the spacing between the spindle and the actuating means. Theactuating means is designed upon operation thereof to engage the spindleduring a first portion of its stroke and thereafter during the remainingportion of the stroke to move the spindle upwardly as viewed, to actuatelever assembly 15 in a clockwise direction to release the brake.

It will be appreciated that numerous mechanical expedients may beemployed to effect this general function. The specifically illustratedmeans embodies a suitable linkage which is actuated by armature member51 of an electromagnet, the coil 52 of which is disposed within theupper magnet housing 31. Specifically, the linkage comprises a bushing53 having bearing supports 54 and 55, which is slidably fitted over thesleeves 38 and 39 on spindle 26. As best seen in Fig. 4, bearingsupports 54 and 55 extend outwardly on opposite sides of bushing 53.Respective pawl levers 56 and 57 are pivotally mounted by means of pins58 and 59 in respective bearing supports 54 and 55. The pins are securedwith respect to the pawl levers by means of headless set screws 60 whichare secured by nuts 61. Diametrically opposite sides of the armature 51are pivotally connected to the ends of pawl levers 56 and 57 byrespective pins 62 and 63 which pass through respective bosses 64 and 65secured to the bottom side of the armature 51 at diametrically oppositepoints.

As will be seen by reference to Fig. 1 and Fig. 4, the armature iscircular in plan form and is provided with a central opening 64a whichclears the linkage. A shim 66 having a central opening thereincorresponding in size to the opening 64a in the armature is fitted tothe top side of the armature. This shim is of non-magnetic material andis utilized to prevent the armature from sticking due to the residualflux in the magnet core after the coil is deenergized.

Pawl levers 56 and 57 are provided with pawl or clutch seats 67 and 68respectively, upon which the pawl or clutch pieces 69 and 70 aresecured. This assembly is disposed above the bearing supports upon thepawl levers and projects upwardly through the opening 64a in thearmature. This is clearly seen in both Figs. 1 and 4.

The faces of the pawl or clutch pieces 69 and 70 which engage thethreaded sleeve 39 are of a configuration corresponding to the surfaceconfiguration of sleeve 39 to assure positive engagement therewith. Inone embodiment the sleeve 39 is provided with threads having a highpitchand the faces of the pawl or clutch pieces are correspondinglyshaped to mesh therewith. The mechanism components, as illustrated,including the magnet and armature, occupy relative positionscorresponding to an energized condition of the electromagnet coil. Inthis position, as shown, the pawl or clutch pieces 69 and 70 are bothengaged with the sleeve 39.

It will be appreciated from a study of the mechanism hereinabovedescribed that the armature for the electromagnet is carried entirely onthe ends of the pawl levers. Thus, when the magnet is deenergized thearmature drops downwardly from the bottom of the magnet core. The forceof the springs 45 and 46 drives the spindle 26 downwardly carrying withit the bushing 53, the pawl lever system and the armature. The movementof bushing 53 downwardly is arrested by a shoulder 71, which is formedon the bushing adjacent its lower end, which engages an adjustable stop72 threaded into the bottom of the lower magnet housing 32. The travelof the bushing between its upper'and lower positions is controlled bythe vertical position of the stop 72 and may be adjusted to any requiredvalue within the illustrated limits. It will be appreciated that suchadjustment controls the open gap position of the armature andthereafter, until further adjustment of the stop is made, this open gapdistance willremain constant.

When the downward travel of bushing 53 is stopped the weight of thearmature on the pawl levers 56 and 57 rotates these leverscounterclockwise and clockwise, respectively, as viewed in Fig. 1, untilsuch time as webs 73 and 74 on pawl levers 56 and 57 respectively abutthe opposite edges of shoulder 71 on the bushing 53. In this positionthe pawl or clutch pieces 69 and 70 are completely disengaged from thethreaded sleeve 39. Consequently, the spindle 26 is released from thearmature controlled pawl or clutch linkage and completes its downwardtravel under the applied force of the compression springs 45 and 46.

The counterclockwise rotation of lever 15 which results from thismovement of the spindle rotates the respective brake arms and the brakeshoes in such directions as to engage the brake shoes with the brakewheel, the spring force being suificient to arrest the brake wheelsrotation for any load up to that of the maximum capacity of the brake.The downward movement of the spindle stops at that time when the torquesapplied to the brake arms by the spring force acting on lever assembly15 is balanced by the resisting torques of the brake arms due toengagement of the brake shoes with the brake wheel. For a giventhickness of brake lining, this point of equilibrium is the maximumdownward position which the spindle 26 will occupy.

As the brake shoe lining wears, the ends of the brake arms which carrythe brake shoes will move closer to the brake wheel. Due to theconnection of the lever assembly 15, with the respective pins 16 and 17on the brake arms, the lever assembly 15 is free to rotate further in acounterclockwise direction. As a consequence, the downward travel of thespindle increases as the brake lining wears. When the armature is in itsfull downward position, the spindle as previously described iscompletely disengaged therefrom and consequently there is no restraintof spindle movement other than due to brake shoe pressure on the brakewheel.

Thus, a relative displacement in the longitudinal position of thespindle with respect to the engaging faces of the pawl or clutch pieces69 and 70 occurs, but there is no change in the dimension between thefaces of the pawl or clutch pieces 69 and 70 and the surface of thethreaded bushing 39 engaged by these pieces. Thus with each stroke ofthe armature upwardly, assuming a certain degree of brake lining wearswith each application of the brake, the pawl pieces 69 and 70 may enga ethe bushing 39 at any point along the length thereof.

Throughout this operation it will be appreciated there is no change inthe travel of the armature. During the first interval of armature travelthe pawl levers 56 and 57 are rotated clockwise and counterclockwiserespectively until the faces of the pawl or clutch pieces 69 and 70engage the threaded sleeve 39. Angular movement of the pawl levers thenstops and continued movement of the armature upwardly, due to itslinkage with the magnetic field of the electromagnet, then carries thespindle 26 and the levers connected thereto, upwardly to move the braketo its released position.

It will now be appreciated that according to the structure of thisinvention means are provided whereby the force which releases the brakehas a definite path of travel and that the length of this path isconstant whether the brake linings are worn evenly or unevenly orcompletely worn out or, whether the brake wheel has expanded from heator contracted from cold. The arrangement is such through the specialcompensating features to pro vide equalized shoe clearance under all ofthe named conditions.

It will be appreciated that the force of the springs decreases with shoelining wear and the spindle moves downwardly a greater distance witheach application of the brake. For that reason the two springs 45 and 46are utilized, one inside the other, the combined scale of which is lowenough so that the variation in torque ranges from high for new liningsto 5% low when the linings are fully worn, giving a total variation intorque of only over the full life of the brake linings.

Suitable means may be provided for indicating the extent of brake liningwear. Such means may be visual and of the form of a scale (not shown)adjacent the spindle Z6. device actuated by the spindle at apredetermined point in downward travel of the spindle 26 or of leverassembly 15, which electrical device controls a suitable audible,visual, or both, signaling device.

Although but one mechanical arrangement embodying this invention hasbeen illustrated herein, it will be appreciated that numerous otherexpedients, in the nature of Other means may involve a suitableelectrical mechanical equivalents, may be employed to achieve theresults herein accomplished. For example in connection with the brakereleasing mechanism, the general requirement therein is that the brakereleasing clutch or pawl system be frictionally released from the brakecontrol lever when the magnet is deenergized, and that there shall besubstantially no relative movement with regard to spacing of the clutchparts as the clutch element connected with the brake control lever movesto new positions with wear of the brake shoe lining. Additionally, theconfiguration of the clutch faces may be subjected to considerablechange depending upon the axial load on spindle 26 and the materialsfrom which the clutch elements are made. Under certain conditions,smooth clutch faces may be utilized with success. While many brakes aredesigned for electric control there are nonetheless many applicationswhere electric control may not be feasible and so other means such ashydraulic or manual force may be utilized to actuate the mechanism.

It is therefore intended that this disclosure shall include such andother equivalent detail variations in the subject matter disclosed andthat such subject matter together with the illustrations of the drawingsshall be considered only as illustrative of the principles of thisinvention and not interpreted in a limiting sense.

The invention claimed is:

1. An electromagnetic device, comprising a core having an openingtherethrough a coil disposed about said core, the axis of said openingsubstantially paralleling the axis of said coil, a rod slidably mountedin said opening, a member slidably fitted over said rod, an armaturehaving an opening therein, said armature being disposed about said rodadjacent said core, and a lever pivotally connected to said armature andto said member, said lever having a portion thereon positivelyengageable with said rod upon movement of said armature toward said corewhen said electromagnet is energized.

2. An electromagnetic device, comprising, a core having an openingtherethrough a coil disposed about said core, the axis of said openingsubstantially paralleling the axis of said coil, a rod slidably mountedin said opening, a member slidably fitted over said rod, an armaturehaving an opening therein, said armature being disposed about said rodadjacent said core, bearing supports on opposite sides of said member, apawl lever pivotally mounted in each bearing support and pivotallyconnected to the armature at another point on the pawl, said pawl beingat times positively engaged with said rod, and a stop for limitingmovement of said member away from said armature.

3. An electromagnetic device, comprising: a core having an openingtherethrough a coil disposed about said core, the axis of said openingsubstantially paralleling the axis of said coil, a rod slidably mountedin said opening, a member slidably fitted over said rod, an armaturehaving an opening therein, said armature being disposed about said rodadjacent said core, a threaded section on said rod, bearing supports onopposite sides of said member, a pawl lever pivotally mounted in eachbearing support and having a face portion of a configuration to fitagainst said threatened section, said face portion being normallydisengaged from said threaded section, and means pivotally connectingeach pawl lever to said armature.

4. An electromagnetic device, comprising: a core having an openingtherethrough, a coil disposed about said core, the axis of said openingsubstantially paralleling the axis of said coil, a rod slidably mountedin said opening, a member slidably fitted over said rod, an armaturehaving an opening therein, said armature being disposed about said rodadjacent said core, a threaded section on said rod, bearing supports onopposite sides of said member, a pawl lever pivotally mounted in eachbearing support and having a face portion of a configuration to fitagainst said threaded section, said face portion being 1 I normallydisengaged from said threaded section, and stop means for limitingmovement of said rod in a direction opposite to movement thereof by saidarmature and pawl levers.

5. An electromagnetic device, comprising: a core having an openingtherethrough, a coil disposed about said core, the axis of said openingsubstantially paralleling the axis of said coil, a rod slidably mountedin said opening, a member slidably fitted over said rod, an armaturehaving. an opening therein, said armature being disposed about said rodadjacent said core, a threaded section on said rod, bearing supports onopposite sides of said member, a pawl lever pivotally mounted in eachbearing support and having a face portion of a configuration to fitagainst said threaded section, said face portion being normallydisengaged from said threaded section, and spring means for biasing saidrod in said opposite direction.

6. An electromagnetic device, comprising: a core having an openingtherethr-ough, a coil disposed about said 20 1,645,628

core, the axis of said opening substantially paralleling the axis ofsaid coil, a rod slid'ably mounted in said} opening, a member slidablyfitted over said rod, an armature having an opening therein, saidarmature being disposed about said rod adjacent said core, a threadedsection on said rod, bearing supports on opposite sides of saidjmember,a pawl lever pivotally mounted in each bearing support and having a faceportion of a configuration to fit against said threaded section, saidface portion being normally disengaged from said threaded section, andmeans for limiting movement of said armature in said opposite direction.

References (Jited in the file of this patent UNITED STATES PATENTS246,956 Knowles Sept. 13, 1881 513,111 Jandus Ian. 23, 1894 1,290,628Mayor Jan. 7, 1919 Smith Oct. 18, 1927

